1. Field of the Invention
The present invention generally relates to the packaging art using pressurized dispensers of the type comprising an outer container and a closure member which includes a valve assembly for controlled dispensing of normally fluid substances, such as cosmetic preparations, glues, solvents, air freshening agents and the like products.
Ecological considerations and legal requirements based thereon call for replacing prior art pressurizing agents, such as halocarbons of the type known as freons, and for replacing metal containers by synthetic organic polymers capable of easy disposal or recycling. The problems of disposal or recycling became solvable with the advent of synthetic organic polymer compositions, such as polyesters including polyethylene terepthalate (PET), and polycarbonates, that can be economically processed by thermal moulding methods and yet are capable of withstanding the internal pressure needed for dispensing of the content upon operation of the valve assembly.
Pressurization, however, with relatively innocuous gaseous pressurizing media such as pressurized air, carbon dioxide, nitrogen and the like, tends to present severe problems. In particular, the use of such compressed gases leads to unusually severe criteria for the sealing quality of the pressurizable containers.
2. Prior Art
In conventional metallic dispensers pressurized with a low boiling liquid medium, such as a halocarbon of the freon type, any gaseous portion of the propellant that has escaped due to use or leakage is compensated by vaporization of liquid propel ant so that an essentially constant pressure is maintained within the dispenser. On the other hand, when using a compressed gas as propellant, a pressure reduction caused by use or leakage cannot be recompensed.
At the same time, with an increasing preference for pressure dispensers made essentially of synthetic organic polymers, sealing interconnection of the valve-carrying lid with the outer container of the dispenser became problematic and even potentially dangerous; increased inner pressure, notably in a hot environment, or careless handling of the dispenser can cause that the valve lid is explosively expelled.
Accordingly, it is known in the art to seal the connection between valve disk and outer container, or between valve disk and valve unit, with a duromeric polymer composition (also termed "thermosetting" even when crosslinking is achieved at normal temperatures). This requires specialized machinery, however, so that the dispensers must be sealed by the manufacturer of the dispenser rather than at the site where the dispenser is filled with a given product.
Pressurizable dispensers made of a synthetic polymer composition and supposed to have a mechanically safe connection between the valve-carrying closure element and the outer container yet providing for filling of the container by the distributor or manufacturer of the product in a conventional manner and at acceptable output rates are disclosed in PCT patent specification W0-88/10221 and in German patent specification DE 3 737 265.
According to W0-88/10221 the closure cup plus valve assembly is welded to the neck of a dispenser made of a synthetic organic polymer composition by means of an ultrasonic process. Attached to the valve at the inner end thereof is a flexible inner pouch in which the filled product can be stored While being hermetically sealed. The product to be filled into the dispenser is pressed through the valve into the vacuumized pouch. In a second process step, propellant is introduced through a filling element or "snorkel" which is fitted onto the valve outlet tube. For this pressurizing step a separate opening is provided which is sealed at its inner side by a sealing element or flap-valve made of an elastomeric material. Such materials tend to be susceptible to aging; upon prolonged contact with oxygen and/or upon the impact of heat they tend to become brittle and generally have a lower resistance against migration or diffusion of the pressuring medium than the material which forms the predominant part of the closure element.
Further, such sealings tend to rapidly loose their effectiveness when exposed to a dusty environment because dust particles may penetrate between the sealing element and the closure element.
DE 3 737 265 discloses a two-way valve. Here again, the product is charged, in a first process step, through the valve into an inner container; in a second process step the valve position is changed and the propellant is injected through another passage of the valve. Again, the opening for pressurizing the container is sealed with a sealing element made of an elastomeric material. Such sealings display the same drawback as described above and are unsatisfactory for pressure dispensers of this type.
A further disadvantage of both prior art dispenser discussed above resides in the fact that charging of the outer or inner container and introduction of the pressurizing medium must be carried out in separate process steps.